maybe css style or html tag
example:
<div style="@prince code qr information" />
or
<code type="qr" value="information" />

something like that

What do you think about this?

You can use JavaScript to generate the QR code!

Yes, but it very slow ...

How slow? And how many QR codes do you need in each document?

> How slow?
~ 1 sec. to document
(without qr-code ~200mc)

> And how many QR codes do you need in each document?
now: 15 000 - 20 000 (monthly)
perspectively: 100 000 (monthly)

one QR code in one document

In the short term, you could generate the documents with QR codes already evaluated in your server framework, if you have a convenient library available. In the long term it would be good to make Prince faster. From 0.2 to 1.0 seconds is not a huge change; what if it was 0.5 seconds? Or 0.8?

1 sec vs 0.5 sec: 30 hours vs 15 hours
it huge changes for my client

Okay true, good point.

Which QR code script are you using?

check following post for creating qr code barcode using javascript. And you can also find some free QR code scanning API in that forum. Very good source.

http://stackoverflow.com/questions/7196798/javascript-api-for-generating-qr-codes